Intelligence transmission in digital form is common in digital radio systems. In these systems, information, typically in the form of an analog signal, produces a digital waveform. The digital waveform, in turn, represents information. This information is sent within a radio system by modulating an RF carrier. However, transmission using such a modulated RF carrier can result in errors in the received signal. These errors may be produced due to interference in the radio transmission. Additional errors may enter the data stream due to the phase of the demodulating frequency. For example, depending on the demodulating frequency phase .phi., the sign of the sine or cosine demodulating sinusoid may be .+-. sine or .+-. cosine (four possibilities).
Additionally, the transmission of the data is in serial form with the information collected in discrete packets. These packets may be in serial form or parallel form. The packets have starting and ending bits and parity or check bits. To properly interpret the data it may be necessary to identify the start or end of each packet, the separate data bit locations in the packet and to correctly interpret the check bit.
In order to determine whether an error has entered the data stream or more particularly a packet in the data stream, the check bit is added. The use of check bits for detecting and correcting errors in the received data is well known. For example, the use of coding bits in connection with digital radio systems is fully discussed, in OPTIMAL CONVOLUTIONAL SELF-ORTHOGONAL CODE WITH AN APPLICATION TO DIGITAL RADIO, (CSOC's) G. D. Martin, AT&T Bell Laboratories, North Andover, Mass. 01845; 1985 IEEE. Other discussions of Convolutional Self-Orthogonal Codes (CSOC's) are Threshold Decoding, J. L. Massey, MIT Press 1963 and New Convolutional Codes, W. W. Wu, Part I IEEE TRANS. COMMUN. COM-23, pages 942-956.
In the past, error correction and packet start definition has been treated as two separate operations. In the operation of a CSOC, the encoding bit is stripped from the data stream leaving the data or information bit stream. The data stream is then reencoded using the same algorithm as used by the transmitter encoder to encode the check bit. The reencoded check bit produced at the receiver is then compared with the transmitted, stripped check bit (for example, in an exclusive OR). The output of the exclusive OR is called a Syndrome bit or "S" bit. The purpose of the Syndrome bit is to indicate whether the check bit received in the data stream by the receiver is the same as the check bit encoded at the transmitter. This indication may be a "T" or "F" bit. These techniques for using the Syndrome bit for error detection and correction in the data stream, as discussed above, are contained within the disclosed references. As use of CSOC's and the generation of Syndrome bits are well known in the art, they are not discussed.